Conventional motion picture film comprises frames that are displayed sequentially at a frame rate of 24 frames per second (24 fps), or 30 fps, or some other rate. Required special effects may embodied in the displayed film.
Systems (including "telecine" systems) have been developed for converting motion picture film into video signals. These systems generate a video signal from motion picture film images by scanning the film frames sequentially to generate digitized film images. They then convert the digitized images into a video signal having a standard video frame rate (25 video frames per second for PAL video, 29.97 video frames per second for NTSC video, or 30 video frames per second for SMPTE-240M high definition video). Each video frame consists of two fields.
In film scanning systems, it is sometimes desirable to mix digital data signals representing digitized images. For example, it is sometimes desirable to generate a composite data signal suitable for conversion into a composite video signal for display as a split screen image on a video monitor.
However, until the present invention, no practical technique had been developed for mixing signals of this type with simple digital circuitry.